SDL2 texture blend help

[Ivan Trombley]

On Wednesday, 13 December 2017 at 13:54:28 UTC, Martin Drašar 
wrote:
> Dne 13.12.2017 v 4:03 Ivan Trombley via Digitalmars-d napsal(a):
>> On Wednesday, 13 December 2017 at 01:44:33 UTC, Dmitry wrote:
>>> On Tuesday, 12 December 2017 at 23:28:23 UTC, Ivan Trombley 
>>> wrote:
>>>> Here's the code that produces the correct results (exactly 
>>>> the same
>>>> as GIMP):
>>> Share images you used, please.
>> 
>> Background image: 
>> http://a4.pbase.com/o10/09/605909/1/166706859.XKZZCnSO.background.png
>> 
>> Foreground image: 
>> http://a4.pbase.com/o10/09/605909/1/166706860.c1yD4VWp.image.png
>> 
>> Composited through SDL: 
>> http://a4.pbase.com/o10/09/605909/1/166706869.wLt9RofY.sdl.png
>> 
>> Composited in GIMP 2.9: 
>> http://a4.pbase.com/o10/09/605909/1/166706870.S01BIhVG.gimp.png
>> 
>> When composited using the code I posted looks exactly like the 
>> GIMP 2.9 image.
>
> I am not sure, about the tool you use to view the images, but 
> on my side (Firefox browser) the sdl and gimp output are very 
> different. Maybe some gamma shenanigans going on? Maybe related 
> to PNG Gamma correction...

Gamma is exactly the problem. A page back I posted some code that 
will overlay the image onto the background by converting the 
source and destination pixels to linear RGB, compositing them and 
then converting the final pixel back to sRGB for display. That 
code produces the same results as GIMP. Now I just need to figure 
out how to make GL_FRAMEBUFFER_SRGB (which is supposed to do the 
right thing in the GPU) work with SDL.